Atrial fibrillation (AF) is the most common cardiac arrhythmia and has high patient morbidity, increases mortality two-fold, and increases health care costs. Each year, about 200,000 Americans are newly diagnosed with AF with a prevalence of several million in the U.S. alone. In the majority of cases, AF has been shown to originate from triggers in the pulmonary veins. Histological studies have shown that those triggers are most commonly located in extensions of left atrial myocardium into the proximal pulmonary veins. Recently, radiofrequency ablation of AF has been introduced as a potentially curative alternative treatment. During the ablation of AF, those myocardial sleeves inside the pulmonary veins are identified indirectly by using the local electrical signals and then ablating a the corresponding recording electrodes in the pulmonary veins. Successful isolation of the pulmonary veins has been reported to have short-term success of eliminating AF in 60-90% of patients. However, recurrence rates of 50% or more are reported in longer-term follow-up evaluations as the muscular bundles progressively reconnect with the rest of the left atrial myocardium. One possible solution would be to use optical coherence tomography (OCT) to enable a direct visualization of the muscular bundles to guide the ablation and confirm the curative tissue necrosis thereafter. Hence, the goal of this project is to develop a diagnostic too comprising of a discretely actuated steerable robotic catheter with an integrated OCT probe with an ultrasonic micromotor for radial OCT imager positioning that will reliably visualize the pulmonary vein sleeves. Additionally, the ability to confirm complete necrosis of the muscular sleeve (after treatment) through OCT imaging will provide an extremely helpful clinical endpoint to the procedure and reduce the risk of long-term treatment failure and muscular reconnection. Hence, in this project, we will: Specific Aim 1: Develop a discretely actuated steerable robotic catheter with an integrated OCT imaging probe and micromotor for radial OCT imager positioning to aid in navigating to the vein for placement of the OCT imaging probe in the region of interest. Furthermore, the catheter will be able to move in 3D with multiple degrees-of-freedom. Specific Aim 2: Establish OCT imaging criteria for identifying myocardial vs. fibrous tissue and ablated vs. normal cardiac tissue in situ in ex vivo sheep hearts. Specific Aim 3: Evaluate the accuracy of robotic catheter with integrated OCT in identifying: a) atrial myocardial extensions into the pulmonary veins in the ex vivo human heart and b) acute radiofrequency ablation (RFA) lesions in sheep cardiac tissue.